Fecal occult blood test is also known as stool occult blood test, hemoccult test, guiaic smear test, gFOBT, or occult blood test. Fecal occult blood is detected by microscopic analysis or by chemical tests for hemoglobin, such as the guiaic test. Normally, stools contain small amounts of blood (2-2.5 mL/day); therefore, test for occult blood detect quantities larger than this. Testing is indicated when clinical symptoms and preliminary blood studies suggest GI bleeding. Additional tests are required to pinpoint the origin of the bleeding.
- To detect gastro intestinal bleeding.
- To aid in the early diagnosis of colorectal cancer.
- Explain the patient that this test detects abnormal GI bleeding.
- Instruct the patient to maintain a high-fiber diet and to refrain from eating red meats, turnips, and horseradish for 48 to 72 hours before the test as well as throughout the collection period.
- Tell the patient that the test usually requires three fecal specimens but that sometimes only one sample is needed.
- Instruct the patient to avoid contaminating the fecal specimen with toilet tissue or urine.
- Notify the laboratory and physician of drugs the patient is taking that may affect test results; it may be necessary to restrict them. If the patient must continue using this drugs, note this on the laboratory request.
- Collect three fecal specimens or a random fecal specimen.
- Obtain specimens from two different areas of each fecal specimen.
- Use a wooden applicator to smear a bit of the fecal specimen on the filter paper supplied with the kit. Or, after performing a digital rectal examination, wipe the finger you used for the examination on a square of the filter paper. Place the filter paper with the fecal smear on a glass plate.
- Remove a reagent tablet from the bottle and immediately replace the cap tightly. Place the tablet in the center of the fecal smear on the filter paper. Add 1 drop of water to the tablet, and allow it to soak in for 5 to 10 seconds. Add a second drop, letting it run from the tablet onto the specimen and filter paper.
- After 2 minutes, the filter paper will turn blue if the test result is positive. Don’t read the color that appears on the tablet itself or develops on the filter paper after the 2-minute period. Note the results and discard the filter paper. Remove and discard your gloves and wash your hands thoroughly.
- Open the flap on the side pack and use a wooden applicator to apply a thin smear of the fecal specimen to the guiaic-impregnated filter paper exposed in a box. Apply a second smear from another part of the specimen to the filter paper exposed in box B.
- Let the specimen dry for 3 to 5 minutes. Open the flap at the near of the slide package and place 2 drops of hematocrit developing solution on the paper over each smear. A positive result yields a blue reaction in 30 to 60 seconds. Record the results and discard the slide package. Remove and discard your gloves and wash your hands thoroughly.
Instant-View Fecal Occult Blood Test
- Add a fecal sample to the collection tube. Shake it to mix the sample with the extraction buffer, and then dispose 4 drops into the sample well of the cassette.
- Results will appear on the test region and the control region of the cassette in 5 to 10 minutes, indicating whether the hemoglobin level is > 0.05 pg/ml of feces.
- Send the specimen to the laboratory or perform the test immediately, depending on which test is used.
- Inform the patient that he may resume his usual diet and medications as ordered.
- Single digital office-based test may not be as accurate as serial home collected test.
- Less than 2.5 ml of blood in feces, resulting in a green reaction.
- GI bleeding, this may result from many disorders, such as varices, a peptic ulcer, carcinoma, ulcerative colitis, dysentery, hemorrhagic disease.
- Failure to observe pretest reactions.
- Failure to test the specimen immediately or to send it to the laboratory immediately after collection.
- Bromides, colchicines, indomethacin, iron preparation, phenylbutazone, rauwolfia derivatives, and steroids (possible increase from GI blood loss).
- Ascorbic acid (false-negative, even with significant bleeding).
- Ingestion of 2 to 5 ml of blood (for example, from bleeding gums).
- Active bleeding from hemorrhoids (possible false-positive results).
image by: cancer.umn.edu